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CENOVUS ENERGY INC. PRODUCT: Steam dilation accelerated start-up SERVICE: Technique to accelerate the start-up of SAGD well pairs
Steam dilation accelerated start-up dramatically cuts in situ oilsands production initiation • By Maurice Smith
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nlike conventional oil well drilling, where penetration of the reservoir results in immediate flow of crude to surface, in the oilsands it may take months of coaxing—via the injection of steam to heat and “melt” the bitumen—before production begins. The three to six months of pumping steam underground typically required to initiate flow in steam assisted gravity drainage (SAGD) operations is a costly investment in time and resources. It’s an unwanted expense that Cenovus Energy Inc. is leading the industry in reducing. Amid the approximately 140 technology development initiatives currently underway to improve its oilsands operations, an early success story has been its steam dilation accelerated start-up technique, which has slashed SAGD start-up times down to three weeks or less, some three to six times faster than the industry average. Primarily, it’s all about pressure. Conventionally, operators pump steam down the horizontal sections of both the upper steam injector well and the lower producing well (about five metres separate the two) and rely on heat conduction to establish “communication” between the two. At that point, a steam chamber has been created, injection into the producer can cease and extraction can begin. Cenovus launched laboratory studies to find a way to quicken the process. The company found that by feeding steam down both wells at high pressure in a controlled manner, it could essentially rearrange the sand grains and thereby increase porosity and water mobility, resulting in early inter-well communications. “In [conventional] circulation start-up, we just circulate steam down both wells. You are just slowly relying on heat conduction—there is no actual mobility, there is no flow
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N E W T E C H M AG A Z I N E . C O M
FAST FLOW By accelerating start-up time of its SAGD well pairs at its Christina Lake in situ oilsands operations, Cenovus wells reach their peak production rates quicker.
that you can have between the wells,” says Maliha Zaman, Cenovus reservoir engineer. “If you increase the pressure, you roll the [sand] grains over, and that extra space that you are creating fills with water. What then happens is, instead of having no mobility, you get a bit of movement that you can start flowing between the wells, and that is what gives you the big speed-up.” The company says the process requires only minimal surface facility modifications. Additional benefits are a reduced steam circulation time and a decrease in cumulative steam to oil ratio—the amount of steam used per barrel of bitumen produced, an important economic indicator in SAGD production, says Jason Abbate, group lead, production engineering. “The steam that you save in the process is significant in comparison to our conventional circulation start-up method,” he says. There have also been indications of improved overall production from the wells, Abbate adds. He cautions, however, that the process is reservoir specific. “It’s really dependent on what the reservoir looks like, what’s above and below our SAGD well pairs. In some instances there is water below the well pairs, and in those cases we can’t use dilation effectively the way we have got it set up currently. We are looking at ways to further innovate the technology and move dilation to the next level, so that we can utilize it on all of our reservoirs.” Cenovus began testing steam dilation accelerated start-up at its Christina Lake oilsands development in 2010 and by the end of 2011, it had been applied to approximately 13 wells. The technology contributed to the industry-leading start-up of the Phase C expansion phase, which reached production capacity within eight months of first production, between two and 12 months sooner than comparable projects, according to Cenovus.
PHOTO: CENOVUS ENERGY INC.
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